Typical surgical tourniquet systems of the prior art include a tourniquet cuff which encircles the limb of a surgical patient and a tourniquet instrument which is releasably connected to an inflatable bladder within the tourniquet cuff through a length of tubing, thereby establishing a gas-tight passageway between the cuff and the tourniquet instrument. The tourniquet instrument contains a pressurized gas source which is used to inflate and regulate the pressure in the tourniquet cuff above a minimum pressure required to stop arterial blood flow distal to the cuff, for a duration suitably long for the performance of a surgical procedure. Many types of surgical tourniquet systems have been described in the prior art, such as those described by McEwen in U.S. Pat. No. 4,469,099, No. 4,479,494, No. 5,439,477 and McEwen and Jameson in U.S. Pat. No. 5,556,415 and No. 5,855,589.
Many studies published in the surgical literature have shown that the safest tourniquet pressure is the lowest pressure that will stop the flow of arterial blood past a specific cuff applied to a specific patient for the duration of that patient's surgery. Such studies have shown that higher tourniquet pressures are associated with higher risks of tourniquet-related injuries to the patient. Therefore, when a tourniquet is used in surgery, surgical staff generally try to use the lowest tourniquet pressure that in their judgment is safely possible. It is well established in the medical literature that the optimal guideline for setting the pressure of a constant-pressure tourniquet is based on “Limb Occlusion Pressure” (LOP). LOP can be defined as the minimum pressure required, at a specific time in a specific tourniquet cuff applied to a specific patient's limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff. The currently established guideline for setting tourniquet pressure based on LOP is that an additional safety margin of pressure is added to the measured LOP, to account for physiologic variations and other changes that may be anticipated to occur normally over the duration of a surgical procedure. Surgical tourniquet systems of the prior art that can automatically measure the LOP of individual surgical patients and that can automatically recommend a tourniquet pressure setting based on measured LOP are described by McEwen in U.S. Pat. No. 5,439,477, by McEwen and Jameson in U.S. Pat. No. 5,556,415, and by McEwen et al. in U.S. Pat. App. No. 20060253150.
Standard cylindrical tourniquet cuffs are ideally suited for application to patients with cylindrical limbs. However, when applied to a patient with a tapered limb, a cylindrical cuff will not optimally match the limb taper, and will typically result in a snug fit proximally and a loose fit distally. Consequently, a cylindrical cuff may prove unable to achieve a bloodless field distal to the cuff at normal pressures or may require a substantially higher and more hazardous inflation pressure to achieve a bloodless field, and when inflated may have a tendency to roll or slide distally on the limb during a surgical procedure. In an effort to match the taper of a patient's limb at a desired cuff location, some tourniquet cuffs of the prior art are designed to have an arcuate shape, and are commonly called contour cuffs. When a contour cuff surrounds a limb having a matching taper, a uniformly snug fit can be achieved between the cuff and the limb from the proximal to distal cuff edges. Wide contour tourniquet cuffs of the prior art have been shown in the surgical literature to substantially reduce pressures required to create a bloodless surgical field distal to the inflated cuff (Younger et al., ‘Wide Contoured Thigh Cuffs and Automated Limb Occlusion Measurement Allow Lower Tourniquet Pressures’, Clin Orthop 428:286-293, 2004). Lower tourniquet pressures are associated in the surgical literature with lower risk of injuries to surgical patients.
In military combat and emergency situations, loss of blood is a major cause of death if the injured person is alone or when medical assistance is not immediately available. The use of a tourniquet to stop blood loss from an injured arm or leg is a well-known technique for preventing death in these situations. Once the primary objective of preventing death due to blood loss is achieved, it is desirable to prevent further injury to the limb due to excessive pressure and time of tourniquet application. To minimize mechanical injury to the blood vessels and other soft tissues beneath the tourniquet, the pressure applied by the tourniquet to the underlying arterial blood vessels should be only slightly higher than the minimum pressure required to stop blood flow in the vessels. A prior-art tourniquet that has been widely used in military and emergency applications is described by McEwen et al. in U.S. Pat. No. 6,746,470.
There is a need for a tourniquet system that can accurately and reliably sense arterial blood flow in a limb near a tourniquet cuff that encircles the limb. This needed tourniquet system would allow blood flow near the tourniquet cuff to be sensed and continuously monitored so that cuff pressure could be maintained near the minimum pressure required to stop blood flow past the cuff, thus increasing safety in surgery and for emergency and military applications.
There is a related need for a tourniquet system that can apply a selected pressure to a selected portion of a limb beneath a tourniquet cuff in response to blood flow sensed in the portion of the limb. This needed system would allow the application of a level of pressure to the selected portion that is sufficient to stop blood flow in the selected portion without requiring the application of the same level of pressure to other portions of the limb beneath the tourniquet cuff, thereby increasing the precision of pressure application and improving safety.